XJ8 Cooling Fans Running On. Help please

[serrate]

Hello all,
I have an XJ8 3.2 and the cooling fans stay running on (at low speed mode) even the A/C is off and the engine switched off. At present, I have them fuse out to prevent from battery drainage or even the whole thing catching fire (I heard of a BMW having it). Anybody can help me to trace which can the fault be. The car runs perfect otherwise, no overheating, no climate contro problems at all, just those 2 do not want to stop! Thanks all in advances, David

[NST]

serrate said:

Hello all,
I have an XJ8 3.2 and the cooling fans stay running on (at low speed mode) even the A/C is off and the engine switched off. At present, I have them fuse out to prevent from battery drainage or even the whole thing catching fire (I heard of a BMW having it). Anybody can help me to trace which can the fault be. The car runs perfect otherwise, no overheating, no climate contro problems at all, just those 2 do not want to stop! Thanks all in advances, David

my xk did some thing very similar turned out to be the thermostat until it failed completely.. after a couple of months. i would change the thermostat first asap.

[serrate]

Many thanks, my mechanic is just ordering one and will replace it in any case to start with. To be honest, this is the last thing I would have thought of, because the temperature stays correct and constant and the car doesn't overheat at all, so no signs of malfunction.
I started looking at switches but cannot find any, don't know which switches switch the fans on and off.
Another clue, the temperature still stays correct with the cooling fans disabled, although I haven't tried in a traffic jam of course. Any more comments will be appreciated, hopefully you are right and the problem goes away tomorrow morning! Thanks again.

[P700DEE]

Disconnecting the fan is a brave move !!! The cooling on the V8 engine is compromised to ensure fast warm up and inadequate circulation will result in warped heads and gasket failure (new engine !!!!!) The classic explanation of the fans running on after switch off is failed thermostat as the car is still trying to cool down. Remember the guage is just a damped three position switch, at bottom cool , mid point warm , red means goodbye engine. Now you might just have a fault in the temperature sender, do the fans come on when you turn the ignition on when cold ? Re-connect the fans as soon as possible.

[serrate]

Thank you very much for help. By the way I have only driven the car to the supermarket 2 miles away in this condition.
I have just carried out the tests you advised:
Fans do not switch on from cold start and the do as soon as the A/C comes on, and then switch off if I switch off the aircon and on again if I switch on the aircon again (they run at low speed). I haven't warmed the engine up enough because I wanted to ask you: is it possible that the thermostat is faulty when the temperature gauge consistently reads spot on in the middle, without any fluctuations up or down, that is with no apparent signs of malfunction?
Many thanks again, your further advice will be much appreciated, car is going to the garage in few hours.

[NST]

serrate said:

I wanted to ask you: is it possible that the thermostat is faulty when the temperature gauge consistently reads spot on in the middle, without any fluctuations up or down, that is with no apparent signs of malfunction?

yes, that is exactly what i experienced. i didn't realise it was the thermostat until engine temp went in to the red (turned engine off straight away). we had been driving the car around (locally) for about 6 weeks, before i realised one day that the thermostat was buggered. then the following day temp needle goes into the red switch engine off straight away and waited for jag assist to replace thermostat.

it has been good ever since.

[serrate]

I replaced the thermostat with Jaguar latest part and the problem remains. The job wasn't wasted though, as we seem to have eliminated all the air locks that the system seemed to have (hoses were very hard, like inflated, and we believe the coolant strength was very low, next to water).
We have then tested the system with the A/C off and works perfect, no malfunction at all. With the A/C on, it does work well when cold, but when hot as soon as I connect the A/C on the fans come on and when swiching the A/C off they stay on up to 7 or 8 minutes even after turning the ignition off. Any clues? What it seems to me is that the problem is not in the cooling system itself. Could it be the pressure switch of the A/C or any other switch or a relay? Anyone of you has experienced something similar?
Unfortunately I am away for the next 2 weeks, so I won't be able to play more at it. Many thanks in advance to all of you for your tips, which I will be trying on my comeback and hopefully get down to the solution !

[SEASPANNER]

Hi there,
any luck with your cooling??? I have an xj8 3.2.sport and it has been dumping coolant from the expansion bottle after stopping the engine,temps all normal and car running fine but it gives the enine coolant low warning after about 2 or 3 short trips.i was wondering if there was a pump which circulates the coolant after the enine stops and while the fan is running.if this pump was not working then the coolant would get real hot and spew out........maybe.....or am i in denial about the threat of head gaskets??????

[Wrldtvlr]

I had this problem last fall with the culprit being the water pump. When it was taken out, the vanes which were plastic were down to a nub thus very little water was being circulated. The water pump was replaced with one with aluminum fins and the thermostat was replaced, to be on the safe side while we were in there, with one that fails in the open position so the engine doesn't burn up if a failure occurs.

Edited by Wrldtvlr on Wednesday 17th September 00:55

[SandorB]

Exactly same symptoms as seaspanner. Bought new water pump, took old one off, guess what - it's fine. Bearing a little on the rough side, but impeller still A1 - no melting etc. You can get it off in less than ten mins. Just put a 15mm socket with extension lever on the bolt holding the tensioning roller -it's left hand thread and this takes off tension - belt comes off and goes back on in an instant. Of course you've already slackened off the water pump pulley, and the rest is child's play. Problem likely to be elsewhere